The cellular and molecular responses of the lung to oxidative stress involve increased expression of antioxidant enzymes and stress-response genes, including the stress-inducible gone heme oxygenase-1 (HO-1). Heme oxygenase (HO) catalyzes the first and rate-limiting step in the catabolism of home to yield equimolar quantities of biliverdin IXa, carbon monoxide (CO), and iron. Our laboratory and others have demonstrated that induction of HO-1 provides cytoprotection both in vivo and in vitro against oxidative stress including but not limited to hyperoxia, ischemia-reperfusion, and endotoxin. The mechanism(s) by which HO-1 provides cytoprotection against oxidant-induced tissue injury is poorly understood. Recent studies highlight the possibility that the gaseous molecule CO, a by-product of HO activity, can mediate cytoprotection against oxidant-induced lung injury. Furthermore, we have established that CO mediates protection via the MKK3/p38 mitogen-activated kinase (MAPK) signaling pathway. We hypothesize that CO mediates HO-1 cytoprotection against endotoxic shock and that the reciprocal effects exerted by CO on p38( and p38( MAPK mediate the reciprocal down-regulation of the pro-inflammatory cytokine TNF-( and the upregulation of the anti-inflammatory cytokine IL-10. Furthermore, we hypothesize that a complex interplay between NF-(B and the NF-(B-dependent gone iNOS regulates CO-induced p38 activation and its functional anti-inflammatory and cytoprotective effects. We will test this hypothesis by addressing the following aims: 1) to identify which of the p38 isoforms ((,(,(,() are involved in the anti-inflammatory effects observed with CO. 2) To determine the role of NF-(B activation and the role of the p38 isoforms in this activation. 3) Evaluate the mechanism by which CO-induced activation of p38 provides cytoprotection in endotoxic shock. 4) Evaluate the rote of CO-induced iNOS in the cytoprotection and induction of the anti-inflammatory phenotype.